Vacuum dehydration apparatus



Jan. 24, 1956 G. H. BANCROFT 2,731,734

VACUUM DEHYDRATION APPARATUS Filed June 9, 1953 2 Sheets-Sheet l GEORGEH. BAA CROFT IN V EN TOR.

ATTORNEYS 3M. 3956 G. H. IBANCROFT 2,731,734

VACUUM DEHYDRATION APPARATUS Filed June 9, 1953 2 Sheets-Sheet 2 Fla?GEORGE H. BAA/CROFT INVENTOR.

ATTORNEYS Uit u? States Patent 2,731,734 VACUUM. DEHYDRATION APPARATUSGeorge H. BancrofhRocliester, N. Y, assiguor, by mesne assignments, toConsolidated Vacuum Corporation, Rochester, N. Y., a corporation of NewYork Application June 9, 1953,.Serial No.- 360,528 4 Claims. (Cl; 34-76)This invention. relates to: apparatus'particularly adapted fordehydrating heat-labile material. under vacuum-..

Vacuum. dehydration is used rather extensively in the processing ofheat-labile materials: such; as Serums, vaccines and the like-Theprocess usually involves freezing the material to be dehydrated? andsubjecting it in the frozen state to a reduced. pressure: below' thevapor pressure of water whereby dehydration is effected by sublimationfrom the frozen state.

It is an object of this invention. vacuum dehydration apparatus.

It is another object of the invention. to. provide improved vacuumdehydration. apparatus constructed. for optimum performance" throughoutthe dehydration process.

A further objectof the invention is to provide vacuum dehydrationapparatus wherein the difficulties; normally attendant upon thedehyc'lration due tochanges in the concentration of water vapor duringthe processing are largely obviated.

Another object of the invention is to provide appara tus wherein maximumpumping capacity and. maximum condensingv capacity are available duringthev evolution of the largest volume of. water vapors, and. wherein theefficiency of evacuation is: atan optimum. level during the final stagesof dehydration.

Another object of the invention. is; to provide.- improved vacuumdehydration apparatus. wherein: the condenser is eifectively employed incondensing: the: largest volume of vapors during the initial stages ofthe dehydration and. is cleared of condensate during; the final. stagesof. the dehydration without impairing or interrupting the progress ofthe process whereby the processing cycles are accelerated.

Another object of the invention is: to provide vacuum dehydrationapparatus particularly" adapted for optimum efiiciency throughoutthevarious stages: of. the processing cycle.

Another object of the invention. is to provide apparatus includingparticular elements combined in a particular new combination of. unusualutility.

Another object of. the invention is to facilitate the vacuum dehydrationof heat-labile materials by the provision of improved apparatus foreffecting; such. dehydration.

Other objects will be apparent. from the drawings and from thedescription and claims whichfollow;

These and other objects: are. attained by means of this invention asfully described hereinafter with particular reference to a preferredembodiment illustrated by the drawings.

Of the drawings:

Fig. 1 is a viewin. elevation, partly broken away andin section, of acomplete vacuum. dehydration unit. consti tuting a preferredembodiment-of-the invention;

Fig, 2 is a section. taken: along. line- 2.-.2. of Fig; 1. andparticularly illustrating the condenser mechanical. pump; and

toprovide improved and, large capacity Fig. 3 is a plan view of theapparatus shown in Fig. l and particularly illustrating the pumpingassembly;

Withparticular reference to the preferred embodiment illustrated in thedrawings, the apparatus embodying the invention: is constructedso asto'be installed at two levels suchason two floors of a processing plant.A dehydration chamber 10, a pair of ejector pumps. 11, 11 and. a

small capacity mechanical vacuum pump 12 are mounted on the upper level,and. a condenser or cold trap 13 and a large capacity mechanical vacuumpump 14 are mounted at the. lower level.

Ejector pumps 1:1, 111 arev mounted in side by side relation adjacentto. chamber 10 and the intake ports of pumps: 11, 11- are. connected totwo legs 16 and 17 of a four-way unioni 18. Chamber 10 is connected;directly with the intake side of pumps 11,. 11 by a. large diameterprimary conduit 19 which is connected to a third leg 20- of' union 18. Alarge diameter branch. conduit 22l connects: primary conduit 19 and withinlet side of cold trap 13.. Valve 23 in primary conduit w betweenbranch conduit 22. and union 1% serves to closeoif conduit19and1isolate'. chamber it from direct connection with pumps 11, 1 1..A. similar valve 24 in branch conduit 22. is: arranged to isolate coldtrap 13 from direct communication with chamber 10.

The outlet sidelofi cold trap 13 is connected to the intake side: ofpumps 11,11 by secondary conduit 25'which is connected to the fourthleg-'26 of. union 18. A valve 28in secondary conduit 25 is arranged toshut off communication between cold trap 13 and pumps 11, 11.

Pumps 11,. 11'. discharge. through outlet conduits Z9 and 30respectively which merge at a. four way fitting 3i. Fitting 31 is: alsoconnected to. a small discharge conduit 32 leading to'the small capacitymechanical vacuum pump 12 and a large. discharge conduit 33 whichconnects with the inletof large capacity mechanical pump 14. A valve 35in dischargeconduit 32 serves to isolate pump 12,v and a. similar vaLve36 in discharge conduit 33 serves to isolate pump 14 from the system. Abypass conduit 37 is com nected to secondary conduitZS between cold trap13 and secondary conduit. valve 23- and discharges intodischargeconduit. 33: leading to the large mechanical pump 14. Bypass. conduit 37is provided with a shut olf valve 38 for breaking. direct connectionbetween: cold trap-13 and pump 14.

The various valves 23-, 24,28, 36 and. are provided with block heaters39,. 39 and thermostats .9, H3 in order to; keep the valves frombecoming frozen. A Pirani gauge 42' or other suitable vacuum. gauge inprimary conduit 19 adjacent. chamber 10,. and. a similar Pirani gauge43- in: secondary conduit 25' allow a continuing measure of the degreeof vacuum within the system.

Dehydration chamber 10- comprises a barrel-like metal shell 44 providedwith a removable end wall. 45: for loading, and unloading the. chamber.Shell 44 and end wall 45 are encased in a heavy layer 46 of insulatingmaterial, and the-entire unit-is mounted on legs 47, 47 which rest.onthe floor. of the upper level v as indicated at 48'. Inside chamber1'0 are the usual racks 49, 49- which carry internal. coils for the:circulation of. controlled temperature brine which is supplied throughinlet line 50 and discharged through outlet. line 51,. both of which areconnected. to a suitable compressor (not shown) for refrigeration.

Cold trap-1-3-comprises apot. shell 52: and removable cover 53 encasedin an. insulating layer 54. andv mounted on legs 55 ,55v which. test onthe-floor of: the lower level as indicated alt-.56. A. plurality ofconcentric, condenser plates 53,. '58 are mounted vertically withinshell. 52. in staggered. relation such. thatt-he inner condenser plateand each alternate plate has its. upper endcontiguousto cover 53 and itslower. end wellspaced from thebottom of shell 52 and the remainder ofplates 58, 58 are mounted with their lower ends contiguous to the bottomof shell 52 and their upper ends spaced from cover 53 The lower end ofbranch conduit 22 opens through cover 53 into the space within theinnermost of condenser plates 58, 58, and secondary conduit 25 opens outof the side of shell 52 outside the outermost condenser plate wherebyvapors entering cold trap 13 must traverse a tortuous path around thecondenser plates to reach the outlet into secondary conduit 25.Condenser plates 58, 58 are fabricated to provide internal fluidchannels 59, 59 for the circulation of refrigerant through the plates,and refrigerant lines 60, 60 connect plates 58, 58 with a compressor(not shown). Spacer tubes 61, 61 maintain proper spacing between plates53, 58 and afford communication between channels 59, 59 in adjacentplates. A drain line 62 opens out of the bottom of shell 52 and istraced with a heater line 63 to free it of ice.

Pumps 11, 11 are desirably of the ejector type employing an organic pumpfluid and comprise the usual boiler 65, ejector tube stack 66, anddiffuser tube 67. Pump fluid vapors generated in the boiler ascend theejector stack and are discharged through a flared ejector nozzle intothe diffuser tube adjacent the intake end of the pump. Pumps 12 and 14are conventional mechanical vacuum pumps such as are Well known in theart.

In operating the apparatus illustrated by the drawings, the material tobe dehydrated is either frozen before introduction into the dehydrationchamber or is placed on the racks in the chamber and frozen bycirculation of refrigerated brine through the coils in the racks. Duringthe initial rough pumping when the greatest volume of vapors is beingevolved, valve 24 in branch conduit 22 and valve 38 in bypass conduit 37are both open, and valve 23 in primary conduit 19, valve 28 in secondaryconduit 25 and valve 36 in discharge conduit 33 are closed whereby thevapor path is out of the chamber through primary conduit 19, into branchconduit 22, through cold trap 13, and thence from secondary conduit 25into bypass conduit 37 and to the large mechanical pump 14. In thisinitial stage of the dehydration cycle, ejector pumps 11, 11 and smallmechanical pump 12 are isolated from the system. Refrigerant circulatedthrough the plates of cold trap 13 effectively freezes out the majorpart of the water vapor and such minor amounts as are drawn into pump 14do not seriously affect its operation since they are progressivelypurged from the pump fluid by operation of the pmup.

When the initial large volume of vapors has been drawn off and thepressure drops to a value where the ejector pumps are necessary, as forexample about 3 mm. pressure, valve 28 in secondary conduit and valve 36in discharge conduit 33 are opened and valve 38 in bypass conduit 37 isclosed. The vapor path is then from chamber 10 into cold trap 13 throughconduits 19 and 22 and thence out secondary conduit 25 to pumps 11, 11which discharge through outlet lines 29 and 30 into discharge conduit 33and thence to large pump 14 which acts as a backing pump for pumps 11,11. This arrangement is maintained until the dehydration cycle nearscompletion. As the volume of gases being pumped decreases, pump 14 canbe cut out of the system by closing valve 36 and the smaller pump 12used as backing pump by opening valve in discharge conduit 32.

When all but a few percent of the moisture has been removed from thematerial being dehydrated, the cold trap 13 is isolated from the systemby closing valve 24 in branch conduit 22 and the ejector pumps 11, 11are connected directly to chamber 10 by opening valve 23 in primaryconduit 19. The low moisture content of the pumped vapors does notdeleteriously aifect the operation of pumps 11, 11 and the pumpingefilciency is increased to optimum by shortening the pumping path andthus greatly lessening the impedance in the system. The small pump 12 isof sufficient capacity to serve efiectively as a backing pump for pumps11, 11 during such direct operation. In the usual dehydrating process,the material being dehydrated can be allowed to warm up during the finalstages of the cycle whereby the vapor pressure of the moisture beingremoved is increased and the dehydration is facilitated.

During the final stages of the dehydration cycle when cold trap 13 isisolated from the system, it can be purged of condensate by circulatingwarm fluid through the condenser plates and drawing off the resultingliquid condensate from the trap through drain 62. In this way, theprocessing of successive batches is facilitated since the cold trap isready for another cycle by the time the material being processed isfinished.

During the processing cycle, the various block heaters 39, 39 serve tomaintain the valves in operating condition. Although the various stagesof the process can be run on a time cycle, it is desirable to follow thecourse of the dehydration and change the pumping combinations accordingto the pressure in the system. This is done by means of Pirani gauges 42and 43.

Thus, the process can be carried out in the following manner. During theinitial stages of the process, the volume of vapors and gases beingpumped will be high and the reading on Pirani gauge 43 will approachatmospheric pressure. When the pressure on gauge 43 begins to drop andapproach the limit of the range of the mechanical pump, little watervapor is getting through the cold trap and pumps 11, 11 can be cut intothe system. The course of the subsequent stages can then be followed ongauge 42 adjacent the chamber. When the pressure on this gauge hasdropped well within the range of the ejector pumps 11, 11 and reaches arelatively steady value, the volume of vapors being evolved is small,and the cold trap can be cut out of the system. The pressure as measuredon gauge 42 will continue downward slowly until a final steady value isreached. Pumping can be continued for a predetermined interval ordiscontinued at this point depending upon the degree of dehydrationdesired, the material being dehydrated and similar variabledeterminants. Similarly, the various stages of the process can be variedin accordance with usual dehydration practices.

The invention thus provides apparatus particularly adapted for effectingvacuum dehydration under optimum conditions throughout the processingcycle, and capable of use in closely spaced recurring cycles ofoperation. The apparatus is adapted for economical operation without thesacrifice of effectiveness, and lends itself to considerable variationin processing techniques and requirements. The apparatus is particularlyadapted for maximum pumping speed and efficiency throughout the widepressure range necessary for effective dehydration and under constantlychanging conditions of vapor evolution.

Although the invention has been described in considerable detail withreference to a preferred embodiment thereof as illustrated in thedrawings, it will be understood that variations and modifications can beelfected within the spirit and scope of the invention as illustrated inthe drawings and described hereinabove and as defined in the appendedclaims.

I claim:

1. Vacuum dehydration apparatus comprising an evacuable dehydrationchamber, high vacuum pumping means disposed adjacent to said chamber, aprimary conduit connecting said chamber directly to the intake side ofsaid high vacuum pumping means, valve means in said primary conduitbetween said chamber and said high vacuum pumping means, condenser meansdisposed adjacent to said chamber, a branch conduit opening directlyfrom said primary conduit into said condenser means, said branch conduitbeing joined to said primary conduit between said chamber and said valvemeans, a secondary conduit opening out of said condenser means remotefrom said branch conduit and connecting said condenser means with theintake side of said high vacuum pumping means, mechanical pumping means,discharge conduit means connecting said mechanical pumping means withthe discharge side of said high vacuum pumping means, valve means insaid discharge conduit means, bypass conduit means connecting saidcondenser means with said mechanical pumping means, and valve means insaid bypass conduit means.

2. Vacuum dehydration apparatus comprising an evacuable dehydrationchamber, high vacuum pumping means disposed laterally from said chamber,a primary conduit connecting said chamber directly with the intake sideof said high vacuum pumping means, condenser means, a branch conduitconnectingsaid primary conduit directly with the inlet of said condensermeans, valve means in said primary conduit between said branch conduitand said high vacuum pumping means, valve means in said branch conduit,a secondary conduit connecting the outlet of said condenser means withthe intake side of said high vacuum pumping means, a mechanical vacuumpump, a second mechanical vacuum pump of smaller capacity than saidfirst-named mechanical vacuum pump, discharge conduit means connectingsaid mechanical vacuum pumps with the discharge side of said high vacuumpumping means, and valve means in said dis charge conduit means forselectively isolating each of said mechanical vacuum pumps from saidhigh vacuum pump ing means.

3. Vacuum dehydration apparatus comprising an evacuable dehydrationchamber, ejector pumping means disposed adjacent to said chamber, astraight primary conduit connecting said chamber directly with theintake side of said ejector pumping means, a vapor condenser, saidcondenser having a central intake port and an outlet port remote fromsaid intake port and having a plurality of concentric condenser elementsarranged in vertically staggered relation for causing vapors to traversea tortuous path from said intake port to said outlet port, a branchconduit connecting said primary conduit with said intake port, valvemeans in said primary conduit and said branch conduit for selectivelyisolating said ejector pumping means and said condenser respectivelyfrom direct connection with said chamber, a secondary conduit connectingthe outlet port of said condenser with the intake side of said ejectorpumping means, valve means for said secondary conduit, a large capacitymechanical vacuum pump, a discharge conduit connecting said large pumpwith the discharge side of said ejector pumping means, a smallercapacity mechanical vacuum pump, a discharge conduit connecting saidsmaller pump with the discharge side of said ejector pumping means,valve means for selectively isolating each of said mechanical pumps fromsaid ejector pumping means, a bypass conduit for connecting saidcondenser directly with said large pump, and valve means for closing offsaid bypass conduit.

4. Vacuum dehydration apparatus comprising an evacuable' dehydrationchamber, high vacuum pumping means disposed adjacent to said chamber, aprimary conduit connecting said chamber directly with the intake side ofsaid high vacuum pumping means, valve means for closing off said primaryconduit, a condenser positioned directly below said primary conduit,said condenser comprising ani evacuable condenser chamber, a pluralityof vertically disposed generally concentric tubular condenser the top ofsaid condenser chamber into the space defined within the innermost ofsaid condenser elements, an outlet port opening out of said condenserchamber outside the vacuum pumping means, valve means for closing saidReferences Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Morse: High Vacuum Technology, Industrial and EngineeringChemistry, vol. 39, #9, September 1947, pages 1064 to 1071, pages 1070and 1071 relied on.

1. VACUUM DEHYDRATION APPARATUS COMPRISING AN EVACUABLE DEHYDRATIONCHAMBER, HIGH VACUUM PUMPING MEANS DISPOSED ADJACENT TO SAID CHAMBER,PRIMARY CONDUIT CONNECTING SAID CHAMBER DIRECTLY TO THE INTAKE SIDE OFSAID VACUUM PUMPING, MEANS, VALVE MEANS IN SAID PRIMARY CONDUIT BETWEENSAID CHAMBER AND SAID HIGH VACUUM PUMPING MEANS, CONDENSER MEANSDISPOSED ADJACENT TO SAID CHAMBER, A BRANCH CONDUIT OPENING DIRECTLYFROM SAID PRIMARY CONDUIT INTO SAID CONDENSER MEANS, SAID BRANCH CONDUITBEING JOINED TO SAID PRIMARY CONDUIT BETWEEN SAID CHAMBER AND SAID VALVEMEANS, A SECONDARY CONDUIT OPENING OUT OF SAID CONDENSER MEANS REMOTEFROM SAID BRANCH CONDUIT AND CONNECTING SAID CONDENSER MEANS WITH THEINTAKE SIDE OF SAID HIGH VACUUM PUMPING MEANS, MECHANICAL PUMPING MEANS,DISCHARGE CONDUIT MEANS CONNECTING SAID MECHANICAL PUMPING MEANS WITHTHE DISCHARGE SIDE OF SAID HIGH VACUUM PUMPING MEANS, VALVE MEANS INSAID DISCHARGE CONDUIT MEANS, BYPASS CONDUIT MEANS CONNECTING SAIDCONDENSER MEANS WITH SAID MECHANICAL PUMPING MEANS, AND VALVE MEANS INSAID BYPASS CONDUIT MEANS.